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Typhoid

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Typhoid is an infectious disease that is spread through contaminated food and water. The burden of typhoid is likely underestimated due to difficulties in surveillance and diagnostic challenges, but recent estimates suggest that there are nearly 12 million cases and more than 128,000 deaths each year. The majority of deaths occur in Asia and sub-Saharan Africa, and young children and adolescents under 15 years of age are disproportionately impacted. Three vaccines are currently recommended by the World Health Organization (WHO). Newly WHO prequalified and recommended typhoid conjugate vaccines (TCVs) have the potential to address some of the shortcomings of the previously available vaccines, which both have limitations that prevent their widespread use in routine immunization programs. Although typhoid is treatable with antibiotics, resistance to commonly used antibiotics is increasing.

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Typhoid disease

  • Typhoid, also known as typhoid fever, is a serious enteric fever caused by the bacterium Salmonella Typhi. It is spread by the fecal-oral route through contaminated food and water, usually due to unimproved sanitation and poor hygiene habits.
  • Symptoms of typhoid include fever, fatigue, headache, and abdominal pain. Other common symptoms include diarrhea or constipation. Symptoms are often mistaken for other diseases such as malaria, pneumonia, dengue fever, influenza, or other febrile illnesses, leading to frequent misdiagnosis.
  • If left untreated, typhoid can cause severe short- and long-term complications such as intestinal perforation, encephalitis, pneumonia, delirium, and severe dehydration, which can be life-threatening.
  • Typhoid has largely been eliminated in industrialized countries due to improved sanitation and antibiotics, but it continues to be a substantial public health issue in much of Asia and sub-Saharan Africa.
  • The burden of typhoid is likely underestimated due to surveillance difficulties and diagnostic challenges, but recent estimates suggest a global burden of nearly 12 million cases and more than 128,000 deaths per year. An estimated 90 percent of typhoid deaths occur in Asia, though recent data from sub-Saharan Africa suggests that the typhoid burden may be greater than previously recognized. Children and adolescents younger than 15 years of age account for the heaviest burden of typhoid cases and deaths.
  • When diagnosed properly, typhoid can be treated with antibiotics, though the rate of cases resistant to available antibiotics is increasing globally. Drug-resistant typhoid is a growing concern, particularly in low- and middle-income countries. An ongoing outbreak in Pakistan, which has sickened more than 850 people, is the first-ever reported extensively drug-resistant typhoid outbreak and is resistant to all but one antibiotic used to treat typhoid. Besides vaccination, other preventative measures include improved water, sanitation, and hygiene among at-risk communities.

Typhoid vaccines

  • Since 2008, two typhoid vaccines have been recommended by WHO to control endemic disease and for use during outbreaks: an oral live attenuated vaccine, Ty21a; and an injectable Vi capsular polysaccharide (ViCPS) vaccine. Ty21a is approved for use in children 2 years and older and requires three to four doses. The ViCPS vaccine is licensed for children 2 years and older with a booster dose required every two to three years. Studies have shown that these two vaccines protect 50 to 80 percent of recipients and are safe, yet exclude the vulnerable cohort of children between 0 and 2 years of age, limiting potential health benefits and inclusion in routine childhood vaccination programs.
  • Newer TCVs overcome many of the limitations of the two previously available vaccines, including longer-lasting protection, fewer required doses, and suitability for children as young as 6 months of age, facilitating their use in routine childhood immunization programs. In 2017, WHO prequalified the first TCV—Typbar-TCV®—signaling that the vaccine meets international standards and allowing it to be procured by United Nations agencies and Gavi, the Vaccine Alliance.
  • In 2018, WHO recommended that typhoid-endemic countries introduce prequalified TCVs into routine childhood immunization programs as a single dose for infants and children over 6 months of age, accompanied by catch-up vaccination campaigns for children up to 15 years of age, where feasible. Additionally, WHO recommended prioritizing countries with a high burden of disease and/or a growing burden of drug-resistant typhoid.
  • Gavi added TCV to its portfolio of vaccines and has earmarked US$85 million to support the introduction of TCVs into routine immunization programs. Applications for financial support are available for Gavi-eligible countries, with introductions anticipated as soon as 2019.
  • Two TCVs are licensed nationally—Typbar-TCV® in India, Nepal, Cambodia, and Nigeria, and PedaTyph™ in India—and several others are in development.

References

Page last updated: August 2018.

Photo: PATH/Janet Shauri.